Pressure-sensitive adhesive composition for optical films, pressure-sensitive adhesive optical film and image display

ABSTRACT

There is provided a pressure-sensitive adhesive composition for optical films. The composition can form a pressure-sensitive adhesive layer that can prevent light leakage caused by stress associated with dimensional change of a component such as an optical film, which include the pressure-sensitive adhesive layer that has reworkability such that it can be easily peeled from a component, and that has satisfactory processability such that it can be processed without pressure-sensitive adhesive stain or dropout, after it is formed on an optical film. A pressure-sensitive adhesive optical film produced using the composition is also provided. The pressure-sensitive adhesive composition includes a (meth)acrylic polymer including (a) 34 to 94% by weight of an alkyl(meth)acrylate monomer unit, (b) 5 to 35% by weight of an aromatic ring-containing (meth)acrylate monomer unit, and (c) 0.01 to 0.5% by weight of an amino group-containing (meth)acrylate monomer unit and further including (d) 0.05 to 3% by weight of a carboxyl group-containing (meth)acrylate monomer unit and/or (e) 0.05 to 2% by weight of a hydroxyl group-containing (meth)acrylate monomer unit and having a weight average molecular weight of 1,600,000 to 3,000,000 as determined by gel permeation chromatography; crosslinking agents including 0.01 to 5 parts by weight of an isocyanate crosslinking agent and 0.01 to 2 parts by weight of a silane coupling agent based on 100 parts by weight of the (meth)acrylic polymer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pressure-sensitive adhesivecomposition required to have durability and light leakage preventiveability for an optical film and to a pressure-sensitive adhesive opticalfilm including an optical film and a pressure-sensitive adhesive layerthat is made from the pressure-sensitive adhesive composition on atleast one side of the optical film. The invention also relates to animage display such as a liquid crystal display and an organicelectroluminescence (EL) display, using the pressure-sensitive adhesiveoptical film. The optical film may be a polarizing plate, a retardationplate, an optical compensation film, a brightness enhancement film, alaminate thereof, or the like.

2. Description of the Related Art

The image-forming mode of liquid crystal displays or the likeessentially requires polarizing elements to be placed on both sides of aliquid crystal cell, and generally polarizing plates are attachedthereto. Besides polarizing plates, a variety of optical elements havebeen used for liquid crystal panels to improve display quality. Forexample, there are used retardation plates for prevention ofdiscoloration, viewing angle expansion films for improvement of theviewing angle of liquid crystal displays, and brightness enhancementfilms for enhancement of the contrast of displays. These films aregenerically called optical films.

When optical members such as the optical films are attached to a liquidcrystal cell, pressure-sensitive adhesives are generally used. Bondingbetween an optical film and a liquid crystal cell or between opticalfilms is generally performed with a pressure-sensitive adhesive in orderto reduce optical loss. In such a case, a pressure-sensitive adhesiveoptical film including an optical film and a pressure-sensitive adhesivelayer previously formed on one side of the optical film is generallyused, because it has some advantages such as no need for a dryingprocess to fix the optical film.

The pressure-sensitive adhesive is required to have somecharacteristics. In some cases, for example, if in the process ofbonding an optical film to a liquid crystal cell, they are misaligned orforeign matter is caught on the bonding surface, the optical film shouldbe separated from the liquid crystal panel so that the liquid crystalcell can be recycled. For this separation process, thepressure-sensitive adhesive should have re-peelability (reworkability)such that the optical film can be easily peeled from the liquid crystalpanel with no adhesive residue. Particularly in recent years, thinliquid crystal panels using chemically-etched glass plates arefrequently used together with conventional panel manufacturingprocesses, and it has become difficult to subject optical films from thethin liquid crystal panels to reworking or processing. Thepressure-sensitive adhesive is also required to have processability suchthat it can be processed without causing adhesive stain or dropout afterit is formed. In addition, the pressure-sensitive adhesive is requirednot to cause any defect in durability tests by heating, moistening andso on, which are generally performed as accelerated environmental tests.Also, the pressure-sensitive adhesive is required to prevent lightleakage caused by dimensional change generated in the pressure sensitiveadhesive layer in the film.

A conventionally proposed method to solve the problems with thereworkability of liquid crystal panels includes adding a plasticizer oran oligomer component to an acrylic polymer used as a base polymer foran acrylic pressure-sensitive adhesive (see Japanese Patent ApplicationLaid-Open (JP-A) No. 2003-329837). However, such an acrylicpressure-sensitive adhesive cannot provide satisfactory reworkability orprocessability for the thin liquid crystal panels.

Other than the above, proposed acrylic pressure-sensitive adhesives foroptical films include an acrylic pressure-sensitive adhesive includingan acrylic polymer produced using alkyl (meth)acrylate, a monomer havinga hydroxyl group in the molecule and a monomer having a functional groupsuch as a carboxyl, amide or amino group in the molecule as monomercomponents (see JP-A No. 2004-091499 and JP-A No. 2004-091500); and apressure-sensitive adhesive including an acrylic polymer produced usingaromatic ring-containing monomer (see Publication of ExaminedApplication No. 62-23287). However, none of these acrylicpressure-sensitive adhesives disclosed in the patent literatures canprovide satisfactory reworkability or processability, although they canprovide improved durability and adhesiveness.

On the other hands, a pressure-sensitive adhesive composition includingplasticizer or oligomers is proposed to prevent light leakage of animage display that is prepared with the use of an optical film (JapanesePatent No. 3594206 and Japanese Patent No. 3533589). However, such apressure-sensitive adhesive composition cannot provide satisfactoryworkability and durability.

A pressure-sensitive adhesive composition for improvements in durabilityand reworkability and remediation of light leakage is proposed, whichincludes a copolymer of an acrylate eater, an aromatic ring-containingmonomer, and a hydroxyl group-containing monomer as a base (see JP-A No.2007-138057 and JP-A No. 2007-1380560). However, such a copolymer doesnot have satisfactory durability, because of its low molecular weightand high degree of dispersion. Such a pressure-sensitive adhesivecomposition is intended to reduce staining or adhesive residue duringre-peeling, but it is not easily peelable and therefore not practicallysatisfactory.

Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No.2003-329837

Patent Document 2: JP-A No. 2004-091499

Patent Document 3: JP-A No. 2004-091500

Patent Document 4: Publication of Examined Application No. 62-23287

Patent Document 5: Japanese Patent No. 3594206

Patent Document 6: Japanese Patent No. 3533589

Patent Document 7: JP-A No. 2007-138057

Patent Document 8: JP-A No. 2007-138056

SUMMARY OF THE INVENTION

An object of the invention is to provide a pressure-sensitive adhesivecomposition for optical films (an optical film pressure-sensitiveadhesive composition) capable of forming a pressure-sensitive adhesivelayer that can prevent light leakage caused by stress associated withdimensional change of a member such as an optical film, that hasreworkability such that an optical film can be easily peeled from aliquid crystal panel with no adhesive residue, and that has satisfactoryprocessability such that it can be processed without pressure-sensitiveadhesive stain or dropout, after it is formed on an optical film.

Another object of the invention is to provide a pressure-sensitiveadhesive optical film including a pressure-sensitive adhesive layerformed from the optical film pressure-sensitive adhesive composition andto provide an image display device with the pressure-sensitive adhesiveoptical film.

As a result of investigations to solve the problems, the inventors havefound the optical film pressure-sensitive adhesive composition describedbelow to complete the invention.

Specifically, the invention is related to a pressure-sensitive adhesivecomposition for an optical film (an optical film pressure-sensitiveadhesive composition), including: a (meth) acrylic polymer including (a)34 to 94% by weight of an alkyl (meth)acrylate monomer unit, (b) 5 to35% by weight of an aromatic ring-containing (meth)acrylate monomerunit, and (c) 0.01 to 0.5% by weight of an amino group-containing(meth)acrylate monomer unit, and further including (d) 0.05 to 3% byweight of a carboxyl group-containing (meth)acrylate monomer unit and/or(e) 0.05 to 2% by weight of a hydroxyl group-containing (meth)acrylatemonomer unit and having a weight average molecular weight of 1,600,000to 3,000,000 as determined by gel permeation chromatography;crosslinking agents including 0.01 to 5 parts by weight of an isocyanatecrosslinking agent and 0.01 to 2 parts by weight of a silane couplingagent based on 100 parts by weight of the (meth)acrylic polymer.

In the pressure-sensitive adhesive composition for an optical film, the(meth)acrylic polymer preferably has a degree of dispersion (Mw/Mn) of 1to 10.

In the pressure-sensitive adhesive composition for an optical film, theamino group-containing (meth)acrylate is preferably a tertiary aminogroup-containing (meth)acrylate.

In the pressure-sensitive adhesive composition for an optical film, theisocyanate crosslinking agent is preferably a polyisocyanate compoundderived from hexamethylene diisocyanate.

In the pressure-sensitive adhesive composition for an optical film, thesilane coupling agent preferably has an acetoacetyl group or an aminogroup.

In the pressure-sensitive adhesive composition for an optical film, thearomatic ring-containing (meth)acrylate is preferably at least oneselected from the group consisting of phenoxyethyl(meth)acrylate andbenzyl(meth)acrylate.

In the pressure-sensitive adhesive composition for an optical film, thephenoxyethyl(meth)acrylate preferably makes up 5 to 20% by weight of allthe monomers constituting the (meth)acrylic polymer.

The invention is also related to a pressure-sensitive adhesive layer foran optical film, including: a product obtained by forming a coating ofany of the optical film pressure-sensitive adhesive compositions statedabove and subjecting the coating to a crosslinking reaction, wherein thecoating has a gel fraction of 55 to 95% and a refractive index of lessthan 1.50 one hour after the formation of the coating.

In the pressure-sensitive adhesive layer for an optical film, thecoating preferably has a gel fraction of 60 to 95% one week after theformation of the coating.

The invention is also related to a pressure-sensitive adhesive opticalfilm, including: an optical film; and any of the above optical filmpressure-sensitive adhesive layers formed on at least one side of theoptical film.

In the pressure-sensitive adhesive optical film, the pressure-sensitiveadhesive layer preferably has a holding power (H) of 20 to 350 μm oneweek after the formation of the pressure-sensitive adhesive layer.

The pressure-sensitive adhesive optical film preferably shows anadhesive force (F1) of 1 N/25 mm to 10 N/25 mm, when it is peeled at apeel angle of 90° and a peel rate of 300 mm/minute after the steps ofmaking it 25 mm wide, bonding it to a alkali-free glass plate throughthe pressure-sensitive adhesive layer by one reciprocation of a 2 kgroller, and allowing it to stand at 23° C. for one hour.

The pressure-sensitive adhesive optical preferably shows an adhesiveforce (F2) of 2 N/25 mm to 15 N/25 mm, when it is peeled at a peel angleof 90° and a peel rate of 300 mm/minute after the steps of making it 25mm wide, bonding it to a alkali-free glass plate through thepressure-sensitive adhesive layer by one reciprocation of a 2 kg roller,and allowing it to stand at 23° C. for one hour and then dried at 60° C.for 48 hours.

The invention is also related to an image display device including atleast one piece of any of the above pressure-sensitive adhesive opticalfilms.

The optical film pressure-sensitive adhesive composition of theinvention includes, as a base polymer, a (meth)acrylic polymer in whichan alkyl(meth)acrylate monomer and an aromatic ring-containing(meth)acrylate are copolymerized in an adequate ratio. This featureprevents light leakage from an optical member produced with the opticalfilm pressure-sensitive adhesive composition. The optical filmpressure-sensitive adhesive composition of the invention also providesimproved processability and reworkability and preventspressure-sensitive adhesive dropout or staining during workingprocesses. The optical film pressure-sensitive adhesive composition ofthe invention also allows easy peeling with no adhesive residue in theprocess of peeling optical films from thin liquid crystal panels,especially from liquid crystal panels using chemically-etched glassplates.

The amino group-containing (meth)acrylate monomer unit present in asmall amount in the (meth)acrylic polymer can improve the stability ofthe crosslink in the pressure-sensitive adhesive layer after thepressure-sensitive adhesive layer is formed by a crosslinking reactionwith the crosslinking agent.

The carboxyl group-containing (meth)acrylate monomer unit and/or thehydroxyl group-containing (meth)acrylate monomer unit present in the(meth)acrylic polymer of the optical film pressure-sensitive adhesivecomposition of the invention also provides improved durability andimproved reworkability. The (meth)acrylic polymer including a carboxylgroup-containing (meth)acrylate or a hydroxyl group-containing(meth)acrylate as a copolymerized component can provide improvedreworkability and improved durability based on the acid-base interactionor the hydrogen bonding of the copolymerized component. It is consideredthat such improvements make it possible to prevent defects such aspeeling off and separation of the pressure-sensitive adhesive underheating or humidifying conditions.

The pressure-sensitive adhesive composition of the invention includingthe prescribed amount of an isocyanate compound as a crosslinking agenthas improved rapid crosslinkability. Specifically, in this case, anaging process after coating may also be omitted. In addition, a silanecoupling agent is used within the prescribed range as anothercrosslinking agent. When the isocyanate compound is used in combinationwith the silane coupling agent, the crosslink stability can beparticularly improved so that the reworkability and the processabilitycan be improved. The pressure-sensitive adhesive also imparts resistanceto damage of panels or rupture of films, when optical members areproduced using it and when the produced optical members are used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described below, the optical film pressure-sensitive adhesivecomposition of the invention includes the monomer units (a) to (c) andfurther includes either one or both of the monomer units (d) and (e).Specifically, it includes, as a base polymer, a (meth)acrylic polymerincluding 34 to 94% by weight of (a) an alkyl(meth)acrylate monomerunit, (b) 5 to 35 parts by weight of an aromatic ring-containing(meth)acrylate monomer unit, and (c) 0.01 to 0.5% by weight of an aminogroup-containing (meth)acrylate monomer unit and further includes (d)0.05 to 3% by weight of a carboxyl group-containing (meth)acrylatemonomer unit and/or (e) 0.05 to 2% by weight of a hydroxylgroup-containing (meth)acrylate monomer unit.

As used herein, the term “alkyl(meth)acrylate” itself simply refers to a(meth)acrylate having a straight or branched chain alkyl group of 2 to18 carbon atoms, which is exclusive of any alkyl(meth)acrylate having anaromatic ring or rings in its structure. The alkyl group preferably hasan average number of carbon atoms of 2 to 14, more preferably of 3 to12, still more preferably of 4 to 9. As used herein, the term“(meth)acrylate” refers to acrylate and/or methacrylate, and has thesame meaning as “meth” with respect to the invention.

Examples of alkyl(meth)acrylate include ethyl(meth)acrylate,n-butyl(meth)acrylate, sec-butyl(meth)acrylate,tert-butyl(meth)acrylate, isobutyl(meth)acrylate,n-pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate,heptyl(meth)acrylate, isoamyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,n-octyl(meth)acrylate, isooctyl(meth)acrylate, n-nonyl(meth)acrylate,isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate,n-dodecyl(meth)acrylate, isomyristyl (meth)acrylate,n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate,stearyl(meth)acrylate, and isostearyl(meth)acrylate. In particular,n-butyl(meth)acrylate and 2-ethylhexyl(meth)acrylate are preferred, andone or more of these materials may be used alone or in combination.

As used herein, the content of the alkyl(meth)acrylate (a) is from 34 to94% by weight, preferably from 50 to 90% by weight, more preferably from70 to 84% by weight, based on the total amount of all the monomercomponents for the(meth)acrylic polymer. If the content of the(meth)acrylic monomer is too low, the adhesion would be undesirablyreduced. The content of the monomer (a) and the content of the aromaticring-containing (meth)acrylate should be balanced.

As used herein, the term “aromatic ring-containing (meth)acrylate”refers to a copolymerizable (meth)acrylate having an aromatic group orgroups in its structure. Examples of the aromatic ring-containing(meth)acrylate (b) include phenyl acrylate, phenoxy(meth)acrylate,phenoxyethyl(meth)acrylate, benzyl(meth)acrylate, phenoxydiethyleneglycol(meth)acrylate, ethylene oxide-modified nonylphenol(meth)acrylate,hydroxyethylated P-naphthol acrylate, and biphenyl(meth)acrylate.Examples thereof also include phenol ethylene oxide-modified(meth)acrylate, 2-naphthoethyl(meth)acrylate, 2-naphthoxyethyl acrylate,2-(4-methoxy-1-naphthoxy)ethyl(meth)acrylate,phenoxypropyl(meth)acrylate, phenoxydiethylene glycol(meth)acrylate,thiol acrylate, pyridyl acrylate, pyrrole acrylate, phenyl acrylate, andpolystyryl(meth)acrylate.

As used herein, the content of the aromatic ring-containing(meth)acrylate (b) is from 5 to 35% by weight, preferably from 10 to 30%by weight, more preferably 15 to 28% by weight, based on the totalamount of all the monomer components for the (meth)acrylic polymer. Thecontent of the aromatic ring-containing (meth)acrylate and the contentof the alkyl(meth)acrylate should be balanced.

As used herein, examples of the amino group-containing (meth)acrylate(c) include monomers other than tertiary amino group-containing(meth)acrylates, such as succinimide-based monomers such asN-(meth)acryloyloxymethylenesuccinimide,N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, andN-(meth)acryloyl-8-oxyoctamethylenesuccinimide; N-substituted amidemonomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide,N,N-diethyl(meth)acrylamide, N,N-diethylmethacrylamide,N-isopropyl(meth)acrylamide, N-methylol(meth)acrylamide,N-methoxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide;

secondary amino group-containing monomers such astert-butylaminoethyl(meth)acrylate; and diacetone(meth)acrylamide,N,N′-methylenebis(meth)acrylamide, N-acryloylmorpholine,N-acryloylpiperidine, N-methacryloylpiperidine, andN-acryloylpyrrolidine. However, tertiary amino group-containing(meth)acrylates are particularly preferred.

Monomers having various tertiary amino groups and (meth)acryloyl groupsare preferably used. The tertiary amino group is preferably tertiaryamino alkyl. The tertiary amino group-containing (meth)acrylate may beN,N-dialkylaminoalkyl(meth)acrylamide or N,N-dialkylaminoalkyl(meth)acrylate. Examples of the tertiary amino group-containing(meth)acrylate include N,N-dimethylaminoethyl(meth)acrylamide,N,N-dimethylaminopropyl(meth)acrylamide,N,N-diethylaminoethyl(meth)acrylamide,N,N-diethylaminopropyl(meth)acrylamide,N,N-dimethylaminoethyl(meth)acrylate,N,N-dimethylaminopropyl(meth)acrylate,N,N-diethylaminoethyl(meth)acrylate, andN,N-diethylaminopropyl(meth)acrylamide.

The amino group-containing (meth)acrylate is used in an amount of 0.01to 0.5% by weight based on the total amount of the monomer componentsused to form the (meth)acrylic polymer. The content of the aminogroup-containing (meth)acrylate is preferably from 0.01 to 0.3% byweight, more preferably from 0.05 to 0.15% by weight. If the content ofthe amino group-containing (meth)acrylate is less than 0.01% by weight,the pressure-sensitive adhesive layer can have poor crosslink stabilityso that satisfactory reworkability or processability cannot be achieved.Such a content is also not preferred in view of durability. On the otherhand, in view of reworkability, the content of the aminogroup-containing (meth)acrylate should not be too high and is controlledto be 0.5% by weight or less.

Any carboxyl group-containing (meth)acrylate having a carboxyl group anda polymerizable functional group with a (meth)acryloyl unsaturateddouble bond may be used without any particular limitations. Examples ofthe carboxyl group-containing (meth)acrylate include (meth)acrylic acid,carboxyethyl(meth)acrylate, and carboxypentyl(meth)acrylate.

The carboxyl group-containing (meth)acrylate may be used in an amount of0.05 to 3% by weight, as needed, based on the total amount of themonomer components forming the (meth)acrylic polymer. The content of thecarboxyl group-containing (meth)acrylate is preferably from 0.05 to 2%by weight, more preferably from 0.1 to 1% by weight. In order to improvedurability, the content of the carboxyl group-containing (meth)acrylateis preferably 0.05% by weight or more. On the other hand, if the contentof the carboxyl group-containing (meth)acrylate is more than 3% byweight, the adhering strength can be undesirably high so that peelstrength can be too high to provide satisfactory reworkability.

Any hydroxyl group-containing (meth)acrylate having a hydroxyl group anda polymerizable functional group having a (meth)acryloyl groupunsaturated double bond may be used without any particular limitations.Examples of the hydroxyl group-containing (meth)acrylate includehydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylate,2-hydroxybutyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate,8-hydroxyoctyl(meth)acrylate, 10-hydroxydecyl(meth)acrylate, and12-hydroxylauryl(meth)acrylate; hydroxyethyl(meth)acrylamide, andothers, such as (4-hydroxymethylcyclohexyl)methyl acrylate,N-methylol(meth)acrylamide, and N-hydroxy(meth)acrylamide.

The hydroxyl group-containing (meth)acrylate may be used in an amount of0.05 to 2% by weight, based on the total amount of the monomercomponents forming the (meth)acrylic polymer. The content of thehydroxyl group-containing (meth)acrylate is preferably from 0.05 to 1.5%by weight, more preferably from 0.1 to 1% by weight. In order to improvedurability, the content of the hydroxyl group-containing (meth)acrylateis preferably 0.05% by weight or more. Particularly when an isocyanatecrosslinking agent is used, the content of the hydroxyl group-containing(meth)acrylate is preferably 0.06% by weight or more in order to ensurecrosslinking points with the isocyanate group. On the other hand, if thecontent of the hydroxyl group-containing (meth)acrylate monomer is toohigh, the adhering strength can be undesirably high so that peeling canbe too low to provide satisfactory reworkability.

Any monomer component other than the monomers described above may beused in an amount of not more than 45% by weight of the total amount ofthe monomers forming the (meth)acrylic polymer, as long as it does notimpair the purposes of the invention. The content of any other monomeris more preferably 40% by weight or less. Examples of such any othermonomer include acid anhydride group-containing monomers such as maleicanhydride and itaconic anhydride; caprolactone adducts of acrylic acid;sulfonic acid group-containing monomers such as styrenesulfonic acid,allylsulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid,(meth)acrylamidepropanesulfonic acid, sulfopropyl(meth)acrylate, and(meth)acryloyloxynaphthalenesulfonic acid; phosphate group-containingmonomers such as 2-hydroxyethylacryloyl phosphate; andalkoxyalkyl(meth)acrylate monomers such as methoxyethyl(meth)acrylateand ethoxyethyl(meth)acrylate.

Examples of additional monomers that may be used include vinyl monomerssuch as vinyl acetate, vinyl propionate, styrene, α-methylstyrene, andN-vinylcaprolactam; epoxy group-containing acrylic monomers such asglycidyl(meth)acrylate; glycol acrylate monomers such as polyethyleneglycol(meth)acrylate, polypropylene glycol(meth)acrylate,methoxyethylene glycol(meth)acrylate, and methoxypolypropyleneglycol(meth)acrylate; and (meth)acrylate ester-based monomers such astetrahydrofurfuryl(meth)acrylate, fluoro(meth)acrylate,silicone(meth)acrylate, and 2-methoxyethyl acrylate.

A copolymerizable monomer other than the above, such as a silane monomerhaving a silicon atom may also be used. Examples of the silane monomerinclude 3-acryloxypropyltriethoxysilane, vinyltrimethoxysilane,vinyltriethoxysilane, 4-vinylbutyltrimethoxysilane,4-vinylbutyltriethoxysilane, 8-vinyloctyltrimethoxysilane,8-vinyloctyltriethoxysilane, 10-methacryloyloxydecyltrimethoxysilane,10-acryloyloxydecyltrimethoxysilane,10-methacryloyloxydecyltriethoxysilane, and10-acryloyloxydecyltriethoxysilane.

In an embodiment of the invention, a (meth)acrylic polymer with a weightaverage molecular weight of 1,600,000 to 3,000,000 is used in view ofdurability, particularly heat resistance. The (meth)acrylic polymer tobe used preferably has a weight average molecular weight of 1,800,000 to2,800,000, more preferably of 2,000,000 to 2,600,000. A weight averagemolecular weight of less than 1,600,000 is not preferred in view of heatresistance. Too high weight average molecular weight can reduce thebonding properties or the adhesive strength and thus is not preferred.The weight average molecular weight refers to values measured by gelpermeation chromatography (GPC) and calculated by converting the weightaverage molecular weight in terms of polystyrene.

In an embodiment of the invention, the (meth)acrylic polymer should havea degree of dispersion between its weight average molecular weight (Mw)and the number average molecular weight (Mn)) in the range of 1 to 10.In view of durability, particularly heat resistance, the degree ofdispersion is particularly preferably from 1 to 8, more preferably from1.5 to 7, still more preferably from 2 to 6. If the degree of dispersionis too high, the content of low molecular weight polymers can increaseso that defects such as foaming could easily occur in a heating test.

For the production of the (meth)acrylic polymer, any appropriate methodmay be selected from known production methods such as solutionpolymerization, bulk polymerization, emulsion polymerization, andvarious radical polymerization methods. The resulting (meth)acrylicpolymer may be any type of copolymer such as a random copolymer, a blockcopolymer and a graft copolymer.

In a solution polymerization process, for example, ethyl acetate,toluene or the like is used as a polymerization solvent. In a specificsolution polymerization process, for example, the reaction is performedunder a stream of inert gas such as nitrogen at a temperature of about50 to about 70° C. for about 5 to about 30 hours in the presence of apolymerization initiator.

Any appropriate polymerization initiator, chain transfer agent,emulsifying agent and so on may be selected and used for radicalpolymerization. The weight average molecular weight of the (meth)acrylicpolymer may be controlled by the amount of addition of thepolymerization initiator or the chain transfer agent or by the reactionconditions. The amount of the addition may be controlled as appropriatedepending on the type of these materials.

Examples of the polymerization initiator include, but are not limitedto, azo initiators such as 2,2′-azobisisobutylonitrile,2,2′-azobis(2-amidinopropane)dihydrochloride, 2,2′-azobis[2-(5-methyl-2-imidazoline-2-yl)propane]dihydrochloride,2,2′-azobis(2-methylpropionamidine)disulfate,2,2′-azobis(N,N′-dimethyleneisobutylamidine), and2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (VA-057,manufactured by Wako Pure Chemical Industries, Ltd.); persulfates suchas potassium persulfate and ammonium persulfate; peroxide initiatorssuch as di(2-ethylhexyl)peroxydicarbonate,di(4-tert-butylcyclohexyl)peroxydicarbonate,di-sec-butylperoxydicarbonate, tert-butylperoxyneodecanoate,tert-hexylperoxypivalate, tert-butylperoxypivalate, dilauroyl peroxide,di-n-octanoyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide,tert-butylperoxyisobutylate, 1,1-di(tert-hexylperoxy)cyclohexane,tert-butylhydroperoxide, and hydrogen peroxide; and redox systeminitiators of a combination of a peroxide and a reducing agent, such asa combination of a persulfate and sodium hydrogen sulfite and acombination of a peroxide and sodium ascorbate.

One of the above polymerization initiators may be used alone, or two ormore thereof may be used in a mixture. The total content of thepolymerization initiator is preferably from about 0.005 to 1 part byweight, more preferably from about 0.02 to about 0.5 parts by weight,based on 100 parts by weight of the monomer.

For example, when 2,2′-azobisisobutyronitrile is used as apolymerization initiator for the production of the (meth)acrylic polymerwith the above weight average molecular weight, the polymerizationinitiator is preferably used in a content of from about 0.06 to 0.2parts by weight, more preferably of from about 0.08 to 0.175 parts byweight, based on 100 parts by weight of the total content of the monomercomponents.

Examples of the chain transfer agent include lauryl mercaptan, glycidylmercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid,2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. One of thesechain transfer agents may be used alone, or two or more thereof may beused in a mixture. The total content of the chain transfer agent ispreferably 0.1 parts by weight or less, based on 100 parts by weight ofthe total content of the monomer components.

Examples of the emulsifier used in emulsion polymerization includeanionic emulsifiers such as sodium lauryl sulfate, ammonium laurylsulfate, sodium dodecylbenzenesulfonate, ammonium polyoxyethylene alkylether sulfate, and sodium polyoxyethylene alkyl phenyl ether sulfate;and nonionic emulsifiers such as polyoxyethylene alkyl ether,polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester,and polyoxyethylene-polyoxypropylene block polymers. These emulsifiersmay be used alone, or two or more thereof may be used in combination.

The emulsifier may be a reactive emulsifier. Examples of such anemulsifier having an introduced radical-polymerizable functional groupsuch as a propenyl group and an allyl ether group include Aqualon HS-10,HS-20, KH-10, BC-05, BC-10, and BC-20 (each manufactured by Dai-ichiKogyo Seiyaku Co., Ltd.) and Adekaria Soap SE10N (manufactured by ADEKACORPORATION). The reactive emulsifier is preferred, because afterpolymerization, it can be incorporated into a polymer chain to improvewater resistance. Based on 100 parts by weight of the total monomercomponent, the emulsifier is preferably used in a content of 0.3 to 5parts by weight, more preferably of 0.5 to 1 parts by weight, in view ofpolymerization stability or mechanical stability.

The pressure-sensitive adhesive composition of the present inventionalso includes a isocyanate compound as a crosslinking agent. Examples ofthe isocyanate compounds include: isocyanate monomers such as tolylenediisocyanate; chlorophenylene diisocyanate, tetramethylene diisocyanate,isophorone diisocyanate; xylylene diisocyanate, diphenylmethanediisocyanate, hydrogenated diphenylmethane diisocyanate, and adduct typeisocyanate compounds obtained by adding the isocyanate monomer to apolyhydroxy alcohol, for example trimethylolpropane; and urehthaneprepolymer type isocyanates obtained by addition reaction of anisocyanurate compound, a burette type compound, in addition thereto aknown polyether polyol, a known polyester polyol, a acryl polyol, apolybutadiene polyol, a polyisoprene polyol and the like. Thepolyisocyanate compound is particularly preferred and at least oneselected from the group consisting of hexamethylene diisocyanate,hydrogenated xylylene diisocyanate, and isophorone diisocyanate, or apolyisocyanate compound derived therefrom. Examples of one selected fromthe group consisting of hexamethylene diisocyanate, hydrogenatedxylylene diisocyanate, and isophorone diisocyanate, or thepolyisocyanate compound derived therefrom include hexamethylenediisocyanate, hydrogenated xylylene diisocyanate, isophoronediisocyanate, polyol-modified hexamethylene diisocyanate,polyol-modified hydrogenated xylylene diisocyanate, trimer typehydrogenated xylylene diisocyanate, and polyol-modified isophoronediisocyanate. The polyisocyanate compounds listed above are preferred,because they can rapidly react with the hydroxyl group and particularlycontribute to rapid crosslinking, in which specifically an acid or abase contained in the polymer can act like a catalyst.

One or more of the isocyanate crosslinking agents may be used alone orin combination. The total content of the isocyanate crosslinking agentis preferably from 0.01 to 5 parts by weight, more preferably from 0.02to 3 parts by weight, even more preferably from 0.05 to 1.5 parts byweight, based on 100 parts by weight of the (meth)acrylic polymer. Acontent of less than 0.01 parts by weight could provide insufficientcohesion and thus is not preferred. A content of more than 5 parts byweight may tend to cause peeling in a durability test and thus is notpreferred.

A silane coupling agent may also be used for the pressure-sensitiveadhesive composition for use in the present invention in order toincrease adhesive strength or durability. Any appropriate known silanecoupling agent may be used.

Examples of silane coupling agents include epoxy group-containing silanecoupling agents such as 3-glycidoxypropyltrimethoxysilane,3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane,and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containingsilane coupling agents such as 3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine andN-phenyl-γ-aminopropyl trimethoxysilane; (meth)acrylic group-containingsilane coupling agents such as 3-acryloxypropyltrimethoxysilane and3-methacryloxypropyltriethoxysilane; and isocyanate group-containingsilane coupling agents such as 3-isocyanatepropyltriethoxysilane. Suchsilane coupling agents are preferably used to increase durability.However, other silane coupling agents can also be used to increasedurability.

The silane coupling agent may be used alone, or two or more thereof maybe used in a mixture. The total content of the silane coupling agent ispreferably from 0.01 to 2 parts by weight, more preferably from 0.02 to1 parts by weight, still more preferably from 0.05 to 0.6 parts byweight, based on 100 parts by weight of the (meth)acrylic polymer. Suchcontent is preferable to improve durability and maintain adhesiveness tooptical parts such as liquid crystal cells.

The pressure-sensitive adhesive composition of the present inventionalso includes a peroxide.

In the present invention, any peroxide capable of generating activeradical species by heating or photoirradiation and promoting thecrosslinking of the base polymer in the pressure-sensitive adhesivecomposition may be appropriately used. In view of workability andstability, a peroxide with a one-minute half-life temperature of 80° C.to 160° C. is preferably used, and a peroxide with a one-minutehalf-life temperature of 90° C. to 140° C. is more preferably used.

Examples of the peroxide for use in the present invention includedi(2-ethylhexyl)peroxydicarbonate (one-minute half-life temperature:90.6° C.), di(4-tert-butylcyclohexyl)peroxydicarbonate (one-minutehalf-life temperature: 92.1° C.), di-sec-butyl peroxydicarbonate(one-minute half-life temperature: 92.4° C.), tert-butylperoxyneodecanoate (one-minute half-life temperature: 103.5° C.),tert-hexyl peroxypivalate (one-minute half-life temperature: 109. 1°C.), tert-butyl peroxypivalate (one-minute half-life temperature:110.30° C.), dilauroyl peroxide (one-minute half-life temperature:116.4° C.), di-n-octanoylperoxide (one-minute half-life temperature:117.40° C.), 1,1,3,3-tetramethylbutylperoxy-2-ethyl hexanoate(one-minute half-life temperature: 124.3° C.),di(4-methylbenzoyl)peroxide (one-minute half-life temperature: 128.2°C.), dibenzoyl peroxide (one-minute half-life temperature: 130.0° C.),tert-butyl peroxyisobutylate (one-minute half-life temperature: 136.1°C.), and 1,1-di(tert-hexylperoxy)cyclohexane (one-minute half-lifetemperature: 149.2° C.). In particular,di(4-tert-butylcyclohexyl)peroxydicarbonate (one-minute half-lifetemperature: 92.1° C.), dilauroyl peroxide (one-minute half-lifetemperature: 116.4° C.), dibenzoyl peroxide (one-minute half-lifetemperature: 130.0° C.), or the like is preferably used, because theycan provide high crosslinking reaction efficiency.

The half life of the peroxide is an indicator of how fast the peroxidecan be decomposed and refers to the time required for the amount of theperoxide to reach one half of its original value. The decompositiontemperature required for a certain half life and the half life timeobtained at a certain temperature are shown in catalogs furnished bymanufacturers, such as “Organic Peroxide Catalog, 9th Edition, May,2003” furnished by NOF CORPORATION.

One or more of the peroxides may be used alone or in combination. Thetotal content of the peroxide is from 0.01 to 2 parts by weight,preferably from 0.04 to 1.5 parts by weight, more preferably from 0.05to 1 part by weight, based on 100 parts by weight of the (meth)acrylicpolymer. To adjust processability, reworkability, crosslink stability,and releasability, the content can be optionally selected.

The amount of decomposition of the peroxide may be determined bymeasuring the peroxide residue after the reaction process by highperformance liquid chromatography (HPLC).

More specifically, for example, after the reaction process, about 0.2 gof each pressure-sensitive adhesive composition is taken out, immersedin 10 ml of ethyl acetate, subjected to shaking extraction at 25° C. and120 rpm for 3 hours in a shaker, and then allowed to stand at roomtemperature for 3 days. Thereafter, 10 ml of acetonitrile is added, andthe mixture is shaken at 25° C. and 120 rpm for 30 minutes. About 10 μlof the liquid extract obtained by filtration through a membrane filter(0.45 μm) is subjected to HPLC by injection and analyzed so that theamount of the peroxide after the reaction process is determined.

An organic crosslinking agent or a polyfunctional metal chelate may alsobe used as the crosslinking agent. Examples of the organic crosslinkingagent include epoxy crosslinking agents, and imine crosslinking agents.The polyfunctional metal chelate may comprise a polyvalent metal and anorganic compound that is covalently or coordinately bonded to the metal.Examples of the polyvalent metal atom include Al, Cr, Zr, Co, Cu, Fe,Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, and Ti. Theorganic compound has a covalent or coordinate bond-forming atom such asan oxygen atom. Examples of the organic compound include alkyl esters,alcohol compounds, carboxylic acid compounds, ether compounds, andketone compounds.

When the pressure-sensitive adhesive layer is formed, not only thecontrol of the amount of addition of these agents but also the effect ofthe crosslinking temperature or the crosslinking time should be welltaken into account.

The crosslinking temperature and the crosslinking time can be controlleddepending on the type of the crosslinking agent to be used. Thecrosslinking temperature is preferably 170° C. or lower.

The crosslinking process may be performed at the temperature where theprocess of drying the pressure-sensitive adhesive layer is performed, oran independent crosslinking process may be performed after the dryingprocess.

The crosslinking time is generally from about 0.2 to about 20 minutes,preferably from about 0.5 to about 10 minutes, while it can bedetermined in view of productivity or workability.

The pressure-sensitive adhesive composition of the present invention mayalso contain any other known additive. For example, a powder such as acolorant and a pigment, a dye, a surfactant, a plasticizer, a tackifier,a surface lubricant, a leveling agent, a softening agent, anantioxidant, an age resister, a light stabilizer, an ultravioletabsorbing agent, a polymerization inhibitor, an inorganic or organicfiller, a metal powder, or a particle- or foil-shaped material may beadded as appropriate depending on the intended use. A redox systemincluding an added reducing agent may also be used in the controllablerange.

The pressure-sensitive adhesive optical film of the present inventionincludes an optical film and a pressure-sensitive adhesive layer that isformed from the pressure-sensitive adhesive on at least one side of theoptical film.

For example, the pressure-sensitive adhesive layer may be formed by amethod that includes applying the pressure-sensitive adhesivecomposition to a release-treated separator or the like, removingpolymerization solvents and so on by drying and curing the compositionto form a pressure-sensitive adhesive layer, and then transferring thepressure-sensitive adhesive layer onto an optical film. Alternatively,the pressure-sensitive adhesive layer may be formed by a method thatincludes directly applying the pressure-sensitive adhesive compositionto an optical film serving as the base material and removingpolymerization solvents and so on by drying and curing the compositionto form a pressure-sensitive adhesive layer on the optical film. Beforethe pressure-sensitive adhesive is applied, one or more optionalsolvents other than the polymerization solvents may be further added tothe pressure-sensitive adhesive.

A silicone peeling off liner is preferably used as the release-treatedseparator. The adhesive composition of the invention may be applied tosuch a liner and dried to form a pressure-sensitive adhesive layer. Inthis process, any appropriate method may be used for drying thepressure-sensitive adhesive, depending on the purpose. A method ofheating and drying the coating film is preferably used. The heating anddrying temperature is preferably from 40° C. to 200° C., more preferablyfrom 50° C. to 180° C., particularly preferably from 70° C. to 170° C.When the heating temperature is set within the range, apressure-sensitive adhesive with a high level of adhesive properties canbe obtained.

Any appropriate drying time may be used as needed. The drying time ispreferably from 5 seconds to 20 minutes, more preferably from 5 secondsto 10 minutes, particularly preferably from 10 seconds to 5 minutes.

The surface of the optical film may also be coated with an anchor layeror subjected to any adhesion-facilitating treatment such as coronatreatment or plasma treatment, before the pressure-sensitive adhesivelayer is formed. The surface of the pressure-sensitive adhesive layermay also be subjected to adhesion-facilitating treatment.

Various methods may be used to form the pressure-sensitive adhesivelayer. Examples of such methods include roll coating, kiss roll coating,gravure coating, reverse coating, roll brush coating, spray coating, diproll coating, bar coating, knife coating, air knife coating, curtaincoating, lip coating, and extrusion coating with a die coater or thelike.

The thickness of the pressure-sensitive adhesive layer is not limited,but for example, from about 1 to 100 μm, preferably from 2 to 50 μm,more preferably from 2 to 40 μm, still more preferably from 5 to 35 μm.

The resulting pressure-sensitive adhesive layer according to theinvention may have a gel fraction of 55 to 95%, preferably of 60 to 95%,more preferably of 70 to 95%, one hour after the coating. The gelfraction falling within such a range means that the crosslinking ratecan be high; dents would be less likely to be generated; and theresulting pressure-sensitive adhesive layer can be free from thegeneration of dents.

The resulting pressure-sensitive adhesive layer according to theinvention may have a gel fraction of 60 to 95%, preferably of 65 to 95%,particularly preferably of 70 to 90%, one week after the coating.

In general, when the gel fraction is too high or low, durability canoften be insufficient. If the gel fraction is too high, thepressure-sensitive adhesive layer can fail to withstand the dimensionalchange of the optical film due to shrinkage or expansion particularlyunder heating conditions so that a defect such as peeling off from aliquid crystal cell could easily occur. If the gel fraction is too low,a defect such as foaming between a liquid crystal cell and thepressure-sensitive adhesive layer could easily occur particularly underheating conditions.

The resulting pressure-sensitive adhesive layer according to theinvention should have a refractive index of less than 1.5. In order toprevent light leakage from an image display device including thepressure-sensitive adhesive layer-containing optical film, thepressure-sensitive adhesive layer preferably has no birefringence. Fromthis point of view, the refractive index is more preferably less than1.496, still more preferably less than 1.492.

The pressure-sensitive adhesive layer of the invention preferably has aholding power (H) of 20 to 350 μm, more preferably of 40 to 300 μm,particularly preferably of 50 to 250 μm, after it is applied to a filmor the like and allowed to stand at room temperature (23° C.) for oneweek. If the holding power is too high or low, durability can beinsufficient. If the holding power is too low, the pressure-sensitiveadhesive layer can fail to withstand the dimensional change of theoptical film due to shrinkage or expansion particularly under heatingconditions so that a defect such as foaming between a liquid crystalcell and the pressure-sensitive adhesive layer could easily occur.

When the pressure-sensitive adhesive layer is exposed, thepressure-sensitive adhesive layer may be protected with a sheet havingundergone release treatment (a separator) before practical use.

Examples of the material for forming the separator include a plasticfilm such as a polyethylene, polypropylene, polyethylene terephthalate,or polyester film, a porous material such as paper, cloth and nonwovenfabric, and an appropriate thin material such as a net, a foamed sheet,a metal foil, and a laminate thereof. In particular, a plastic film ispreferably used, because of its good surface smoothness.

The plastic film may be any film capable of protecting thepressure-sensitive adhesive layer, and examples thereof include apolyethylene film, a polypropylene film, a polybutene film, apolybutadiene film, a polymethylpentene film, a polyvinyl chloride film,a vinyl chloride copolymer film, a polyethylene terephthalate film, apolybutylene terephthalate film, a polyurethane film, and anethylene-vinyl acetate copolymer film.

The thickness of the separator is generally from about 5 to about 200μm, preferably from about 5 to about 100 μm. If necessary, the separatormay be treated with a release agent such as a silicone, fluorine,long-chain alkyl, or fatty acid amide release agent, or may be subjectedto release and antifouling treatment with silica powder or to antistatictreatment of coating type, kneading and mixing type, vapor-depositiontype, or the like. In particular, if the surface of the separator isappropriately subjected to release treatment such as silicone treatment,long-chain alkyl treatment, and fluorine treatment, the releasabilityfrom the pressure-sensitive adhesive layer can be further increased. Thepressure-sensitive adhesive layer of the present invention is suitablefor a release-treated separator and particularly suitable for aseparator release-treated with a silicone material.

In the above production method, the release-treated sheet may be usedwithout modification as a separator for the pressure-sensitive adhesivesheet, the pressure-sensitive adhesive optical film or the like, so thatthe process can be simplified.

The optical film may be of any type for use in forming image displayssuch as liquid crystal displays. For example, a polarizing plate isexemplified as the optical film. A polarizing plate including apolarizer and a transparent protective film provided on one or bothsides of the polarizer is generally used.

A polarizer is not limited especially but various kinds of polarizer maybe used. As a polarizer, for example, a film that is uniaxiallystretched after having dichromatic substances, such as iodine anddichromatic dye, absorbed to hydrophilic high molecular weight polymerfilms, such as polyvinyl alcohol type film, partially formalizedpolyvinyl alcohol type film, and ethylene-vinyl acetate copolymer typepartially saponified film; polyene type alignment films, such asdehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride,etc. may be mentioned. In these, a polyvinyl alcohol type film on whichdichromatic materials such as iodine, is absorbed and aligned afterstretched is suitably used. Although thickness of polarizer is notespecially limited, the thickness of about 5 to 80 μm is commonlyadopted.

A polarizer that is uniaxially stretched after a polyvinyl alcohol typefilm dyed with iodine is obtained by stretching a polyvinyl alcohol filmby 3 to 7 times the original length, after dipped and dyed in aqueoussolution of iodine. If needed the film may also be dipped in aqueoussolutions, such as boric acid and potassium iodide, which may includezinc sulfate, zinc chloride. Furthermore, before dyeing, the polyvinylalcohol type film may be dipped in water and rinsed if needed. Byrinsing polyvinyl alcohol type film with water, effect of preventingun-uniformity, such as unevenness of dyeing, is expected by makingpolyvinyl alcohol type film swelled in addition that also soils andblocking inhibitors on the polyvinyl alcohol type film surface may bewashed off. Stretching may be applied after dyed with iodine or may beapplied concurrently, or conversely dyeing with iodine may be appliedafter stretching. Stretching is applicable in aqueous solutions, such asboric acid and potassium iodide, and in water bath.

A thermoplastic resin with a high level of transparency, mechanicalstrength, thermal stability, moisture blocking properties, isotropy, andthe like may be used as a material for forming the transparentprotective film.

Examples of such a thermoplastic resin include cellulose resins such astriacetylcellulose, polyester resins, polyethersulfone resins,polysulfone resins, polycarbonate resins, polyamide resins, polyimideresins, polyolefin resins, (meth)acrylic resins, cyclic olefin polymerresins (norbornene resins), polyarylate resins, polystyrene resins,polyvinyl alcohol resins, and any mixture thereof. The transparentprotective film is generally laminated to one side of the polarizer withthe adhesive layer, but thermosetting resins or ultraviolet curingresins such as (meth)acrylic, urethane, acrylic urethane, epoxy, orsilicone resins may be used to other side of the polarizer for thetransparent protective film. The transparent protective film may alsocontain at least one type of any appropriate additive. Examples of theadditive include an ultraviolet absorbing agent, an antioxidant, alubricant, a plasticizer, a release agent, an anti-discoloration agent,a flame retardant, a nucleating agent, an antistatic agent, a pigment,and a colorant. The content of the thermoplastic resin in thetransparent protective film is preferably from 50 to 100% by weight,more preferably from 50 to 99% by weight, still more preferably from 60to 98% by weight, particularly preferably from 70 to 97% by weight. Ifthe content of the thermoplastic resin in the transparent protectivefilm is 50% by weight or less, high transparency and other propertiesinherent in the thermoplastic resin can fail to be sufficientlyexhibited.

Moreover, as is described in JP-A No. 2001-343529 (WO 01/37007), polymerfilms, for example, resin compositions including (A) thermoplasticresins having substituted and/or non-substituted imido group insidechain, and (B) thermoplastic resins having substituted and/ornon-substituted phenyl and nitrile group in sidechain may be mentioned.As an illustrative example, a film may be mentioned that is made of aresin composition including alternating copolymer comprisingiso-butylene and N-methyl maleimide, and acrylonitrile-styrenecopolymer. A film comprising mixture extruded article of resincompositions etc. may be used. Since the films are less in retardationand less in photoelastic coefficient, faults such as unevenness due to astrain in a polarizing plate can be removed and besides, since they areless in moisture permeability, they are excellent in durability underhumidified environment.

Thickness of the transparent protective film can be properly determinedand generally in the range of from about 1 to 500 μm from the viewpointof a strength, workability such as handlability, requirement for a thinfilm and the like. Especially, the thickness is preferably in the rangeof from 1 to 300 μm and more preferably in the range of from 5 to 200μm. Therefore, it is particularly preferred that the transparentprotective film has a thickness of 5 to 150 μm.

Note that in a case where the transparent protective films are providedon both sides of a polarizer, the protective films made from the samepolymer may be used on both sides thereof or alternatively, theprotective films made from polymer materials different from each othermay also be used on respective both sides thereof.

At least one selected from a cellulose resin, a polycarbonate resin, acyclic polyolefin resin, and a (meth)acrylic resin is preferably usedfor the transparent protective film according to the present invention.

The cellulose resin is an ester of cellulose and a fatty acid. Examplesof such a cellulose ester resin include triacetyl cellulose, diacetylcellulose, tripropionyl cellulose, dipropionyl cellulose, and the like.In particular, triacetyl cellulose is preferred. Much commerciallyavailable triacetyl celluloses are placing on sale and are advantageousin view of easy availability and cost. Examples of commerciallyavailable products of triacetyl cellulose include UV-50, UV-80, SH-80,TD-80U, TD-TAC, and UZ-TAC (trade names) manufactured by FujifilmCorporation, and KC series manufactured by Konica Minolta. In general,these triacetyl cellulose products have a thickness directionretardation (Rth) of about 60 nm or less, while having an in-planeretardation (Re) of almost zero.

Cellulose resin films with relatively small thickness directionretardation may be obtained by processing any of the above celluloseresins. Examples of the processing method include a method that includeslaminating a general cellulose-based film to a base film such as apolyethylene terephthalate, polypropylene, or stainless steel film,coated with a solvent such as cyclopentanone or methyl ethyl ketone,drying the laminate by heating (for example, at 80 to 150° C. for 3 to10 minutes) and then separating the base film; and a method thatincludes coating a general cellulose resin film with a solution of anorbornene resin, a (meth)acrylic resin or the like in a solvent such ascyclopentanone or methyl ethyl ketone, drying the coated film by heating(for example, at 80 to 150° C. for 3 to 10 minutes), and then separatingthe coating.

The cellulose resin film with a relatively small thickness directionretardation to be used may be a fatty acid cellulose resin film with acontrolled degree of fat substitution. While triacetyl cellulose forgeneral use has a degree of acetic acid substitution of about 2.8,preferably, the degree of acetic acid substitution is controlled to 1.8to 2.7, so that the Rth can be reduced. The Rth may also be controlledto be low by adding a plasticizer such as dibutyl phthalate,p-toluenesulfonanilide, and acetyl triethyl citrate, to the fattyacid-substituted cellulose resin. The plasticizer is preferably added inamount of 40 parts by weight or less, more preferably of 1 to 20 partsby weight, still more preferably of 1 to 15 parts by weight, to 100parts by weight of the fatty acid cellulose resin.

For example, the cyclic polyolefin resin is preferably a norborneneresin. Cyclic olefin resin is a generic name for resins produced bypolymerization of cyclic olefin used as a polymerizable unit, andexamples thereof include the resins disclosed in JP-A Nos. 01-240517,03-14882, and 03-122137. Specific examples thereof include ring-opened(co)polymers of cyclic olefins, addition polymers of cyclic olefins,copolymers (typically random copolymers) of cyclic olefins and Q-olefinssuch as ethylene and propylene, graft polymers produced by modificationthereof with unsaturated carboxylic acids or derivatives thereof, andhydrides thereof. Examples of the cyclic olefin include norbornenemonomers.

Various commercially available cyclic polyolefin resins are placing onsale. Examples thereof include Zeonex (trade name) and Zeonor (tradename) series manufactured by Zeon Corporation, Arton (trade name) seriesmanufactured by JSR Corporation, Topas (trade name) series manufacturedby Ticona, and Apel (trade name) series manufactured by MitsuiChemicals, Inc.

The (meth)acrylic resin preferably has a glass transition temperature(Tg) of 1 15° C. or more, more preferably of 120° C. or more, still morepreferably of 125° C. or more, particularly preferably of 130° C. ormore. If the Tg is 115° C. or more, the resulting polarizing plate canhave good durability. The upper limit to the Tg of the (meth)acrylicresin is preferably, but not limited to, 170° C. or less, in view offormability and the like. The (meth)acrylic resin can form a film withan in-plane retardation (Re) of almost zero and a thickness directionretardation (Rth) of almost zero.

Any appropriate (meth)acrylic resin may be used as long as theadvantages of the present invention are not reduced. Examples of such a(meth)acrylic resin include poly(meth)acrylate such as poly(methylmethacrylate), methyl methacrylate-(meth)acrylic acid copolymers, methylmethacrylate-(meth)acrylate copolymers, methylmethacrylate-acrylate-(meth)acrylic acid copolymers,methyl(meth)acrylate-styrene copolymers (such as MS resins), andalicyclic hydrocarbon group-containing polymers (such as methylmethacrylate-cyclohexyl methacrylate copolymers and methylmethacrylate-norbornyl(meth)acrylate copolymers). Poly(C₁₋₆alkyl(meth)acrylate) such as poly(methyl(meth)acrylate) is preferred,and a methyl methacrylate-based resin mainly composed of a methylmethacrylate unit (50 to 100% by weight, preferably 70 to 100% byweight) is more preferred.

Examples of the (meth)acrylic resin include Acrypet VH and AcrypetVRL20A each manufactured by Mitsubishi Rayon Co., Ltd., (meth)acrylicresins having a ring structure in their molecule as disclosed in JP-ANo. 2004-70296, and high-Tg (meth)acrylic resins produced byintramolecular crosslinking or intramolecular cyclization reaction.

Lactone ring structure-containing (meth)acrylic resins may also be used,because they have high heat resistance and high transparency and alsohave high mechanical strength after biaxially stretched.

Examples of the lactone ring structure-containing (meth)acrylic reinsinclude the lactone ring structure-containing (meth)acrylic reinsdisclosed in JP-A Nos. 2000-230016, 2001-151814, 2002-120326,2002-254544, and 2005-146084.

The lactone ring structure-containing (meth)acrylic reins preferablyhave a ring structure represented by Formula (I):

wherein R¹, R² and R³ each independently represent a hydrogen atom or anorganic residue of 1 to 20 carbon atoms. The organic residue may containan oxygen atom(s).

The content of the lactone ring structure represented by Formula (I) inthe lactone ring structure-containing (meth)acrylic resin is preferablyfrom 5 to 90% by weight, more preferably from 10 to 70% by weight, stillmore preferably from 10 to 60% by weight, particularly preferably from10 to 50% by weight. If the content of the lactone ring structurerepresented by Formula (I) in the lactone ring structure-containing(meth)acrylic resin is less than 5% by weight, its heat resistance,solvent resistance or surface hardness can be insufficient. If thecontent of the lactone ring structure represented by Formula (I) in thelactone ring structure-containing (meth)acrylic resin is more than 90%by weight, its formability or workability can be poor.

The lactone ring structure-containing (meth)acrylic resin preferably hasa mass average molecular weight (also referred to as weight averagemolecular weight) of 1,000 to 2,000,000, more preferably of 5,000 to1,000,000, still more preferably of 10,000 to 500,000, particularlypreferably of 50,000 to 500,000. A mass average molecular weight outsidethe above range is not preferred in view of formability or workability.

The lactone ring structure-containing (meth)acrylic resin preferably hasa Tg of 115° C. or more, more preferably of 120° C. or more, still morepreferably of 125° C. or more, particularly preferably of 130° C. ormore. For example, the resin with a Tg of 115° C. or more can producegood durability, when it is incorporated in the form of a transparentprotective film in a polarizing plate. The upper limit to the Tg of thelactone ring structure-containing (meth)acrylic resin is preferably, butnot limited to, 170° C. or less in view of formability and the like.

The total light transmittance of the lactone ring structure-containing(meth)acrylic resin, which may be measured according to ASTM-D-1003 withrespect to injection molded products, is preferably as high as possible,and specifically, it is preferably 85% or more, more preferably 88% ormore, still more preferably 90% or more. The total light transmittanceis an index of transparency, and a total light transmittance of lessthan 85% can result in reduced transparency.

The transparent protective film may be subjected to surface modificationtreatment before it is applied with the adhesive to improve adhesivenessto polarizer. Specific examples of such treatment include coronatreatment, plasma treatment, ozone treatment, flame treatment, primertreatment, glow treatment, saponification treatment, and coupling agenttreatment.

A hard coat layer may be prepared, or antireflection processing,processing aiming at sticking prevention, diffusion or anti glare may beperformed onto the face on which the polarizing film of the abovedescribed transparent protective film has not been adhered.

Further an optical film of the present invention may be used as otheroptical layers, such as a reflective plate, a anti-transflective plate,a retardation plate (a half wavelength plate and a quarter wavelengthplate included), and a viewing angle compensation film, which may beused for formation of a liquid crystal display etc. These are used inpractice as an optical film, or as one layer or two layers or more ofoptical layers laminated with polarizing plate.

The pressure-sensitive adhesive optical film of the present invention ispreferably used to form various types of image displays such as liquidcrystal displays. Liquid crystal displays may be formed according toconventional techniques. Specifically, liquid crystal displays aregenerally formed by appropriately assembling a liquid crystal cell andthe pressure-sensitive adhesive optical film and optionally othercomponent such as a lighting system and incorporating a driving circuitaccording to any conventional technique, except that thepressure-sensitive adhesive optical film of the present invention isused. Any type of liquid crystal cell may also be used such as a TNtype, an STN type, a π type a VA type and IPS type.

Suitable liquid crystal displays, such as liquid crystal display withwhich the pressure-sensitive adhesive optical film has been located atone side or both sides of the liquid crystal cell, and with which abacklight or a reflective plate is used for a lighting system may bemanufactured. In this case, the optical film may be installed in oneside or both sides of the liquid crystal cell. When installing theoptical films in both sides, they may be of the same type or ofdifferent type. Furthermore, in assembling a liquid crystal display,suitable parts, such as diffusion plate, anti-glare layer,antireflection film, protective plate, prism array, lens array sheet,optical diffusion plate, and backlight, may be installed in suitableposition in one layer or two or more layers.

The pressure-sensitive adhesive optical film of the invention may havean adhering strength as described below. Specifically, thepressure-sensitive adhesive optical film preferably shows an adheringstrength (F1) of 1 N/25 mm to 10 N/25 mm, more preferably of 1 N/25 mmto 8.5 N/25 mm, particularly preferably of 2 N/25 mm to 7 N/25 mm, whenit is peeled at a peel angle of 90° and a peel rate of 300 mm/minuteafter the steps of making it 25 mm wide, bonding it to a alkali-freeglass plate through the pressure-sensitive adhesive layer by onereciprocation of a 2 kg roller, and allowing it to stand at 23° C. for 1hour.

The pressure-sensitive adhesive optical film also preferably shows anadhering strength (F2) of 2 N/25 mm to 15 N/25 mm, more preferably of 2N/25 mm to 12 N/25 mm, particularly preferably of 3 N/25 mm to 10 N/25mm, when it is peeled at a peel angle of 90° and a peel rate of 300mm/minute after the steps of making it 25 mm wide, bonding it to aalkali-free glass plate through the pressure-sensitive adhesive layer byone reciprocation of a 2 kg roller, and allowing it to stand at 23° C.for 1 hour and then dried at 60° C. for 48 hours.

EXAMPLE

The invention is more specifically described using the examples below,which are not intended to limit the scope of the invention. In eachexample, “part or parts” and “%” are all by weight. Unless otherwisespecified, standing conditions at room temperature are 23° C. and 65% RH(for 1 hour or 1 week) in each case. The evaluation items in theexamples and so on were measured as described below.

Measurement of Weight Average Molecular Weight

The weight average molecular weight of the resulting (meth)acrylicpolymer was measured by gel permeation chromatography (GPC). The samplewas dissolved in dimethylformamide to form a 0.1% by weight solution.The solution was allowed to stand overnight and then filtered through a0.45 μm membrane filter, and the resulting filtrate was used under thefollowing conditions: analyzer, HLC-8120GPC manufactured by TosohCorporation; column, Super AWM-H, AW4000, AW2500, manufactured by TosohCorporation; column size, each 6.0 mmφ×150 mm; eluent, adimethylformamide solution of 30 mM lithium bromide and 30 mM phosphoricacid; flow rate, 0.4 ml/minute; detector, Refractive index detector(RI); column temperature, 40° C.; injection volume, 20 μl.

Measurement of Number Average Molecular Weight

The number average molecular weight of the resulting (meth)acrylicpolymer was also measured and calculated by gel permeationchromatography (GPC) similar to that described above.

Preparation of Polarizing Plate

An 80 μm-thick polyvinyl alcohol film was stretched to 3 times betweenrolls different in velocity ratio, while it was dyed in a 0.3% iodinesolution at 30° C. for 1 minute. The film was then stretched to a totaldraw ratio of 6 times, while it was immersed in an aqueous solutioncontaining 4% of boric acid and 10% of potassium iodide at 60° C. for0.5 minutes. The film was then washed by immersion in an aqueoussolution containing 1.5% of potassium iodide at 30° C. for 10 secondsand then dried at 50° C. for 4 minutes to give a polarizer. Saponifiedtriacetylcellulose films each with a thickness of 80 μm were bonded toboth sides of the polarizer with a polyvinyl alcohol-based adhesive toform a polarizing plate.

Production Example 1

Production of Acrylic Polymer

To a four-neck flask equipped with a stirring blade, a thermometer, anitrogen gas introducing tube, and a condenser were added 80.1 parts ofbutyl acrylate, 19 parts of phenoxyethyl acrylate, 0.1 part ofN,N-dimethylaminoethyl acrylate, 0.3 part of acrylic acid, 0.5 part of4-hydroxybutyl acrylate, and 0.1 part of 2,2′-azobisisobutyronitrile asa polymerization initiator, with 200 parts of ethyl acetate. Nitrogengas was introduced to replace the air, while the mixture was gentlystirred, and then a polymerization reaction was performed for 6 hours,while the temperature of the liquid in the flask was kept at about 55°C., so that a solution of an acrylic polymer was prepared. After thepolymerization was completed, ethyl acetate was added to provide asolids content of 13% so that an acrylic polymer solution was prepared.

Production Examples 2 to 29

Acrylic polymer solutions were prepared using the process of ProductionExample 1, except that at least one of the type and the amount of themonomer components was changed as shown in Table 1. The weight averagemolecular weight, the degree of dispersion, and the refractive index ofthe acrylic polymer obtained in each example are shown in Table 1.

Example 1

Production of Pressure-Sensitive Adhesive Layer-Carrying PolarizingPlate

Based on 100 parts of the solids of the acrylic polymer solutionobtained in Production Example 1, 0.35 parts of polyol-modifiedhexamethylene diisocyanate (D160N manufactured by Mitsui TakedaPolyurethane Inc.) as a crosslinking agent and 0.2 part of a silanecoupling agent (KBM573 manufactured by Shin-Etsu Chemical Co., Ltd.)were added to the acrylic polymer solution so that an acrylicpressure-sensitive adhesive solution was prepared.

The acrylic pressure-sensitive adhesive solution was then applied to oneside of a silicone-treated polyethylene terephthalate (PET) film (MRF38manufactured by Mitsubishi Polyester Film Corporation) so as to providea pressure-sensitive adhesive layer with a thickness of 20 μm afterdrying. The acrylic pressure-sensitive adhesive solution was then driedat 155° C. for 2 minutes to form a pressure-sensitive adhesive layer.The pressure-sensitive adhesive layer was transferred and bonded to thepolarizing plate so that a pressure-sensitive adhesive layer-carryingpolarizing plate was prepared.

Examples 2 to 27 and Comparative Examples 1 to 12

Pressure-sensitive adhesive layer-carrying polarizing plates wereprepared using the process of Example 1, except that the type or theamount of the acrylic polymer solution, the type or the amount of thecrosslinking agent, or the type or the amount of the silane couplingagent for the preparation of the acrylic pressure-sensitive adhesivesolution was changed as shown in Table 2.

The pressure-sensitive adhesive layer-carrying polarizing plate (sample)obtained in each of the examples and the comparative examples wasevaluated as described below. The results of the evaluation are shown inTable 2.

Measurement of Initial Adhesive Force

The sample was cut into 25 mm-wide pieces (120 m in length). Each samplepiece was then press-bonded to a 0.7 mm-thick alkali-free glass plate(1737 manufactured by Corning Incorporated) by one reciprocation of a 2kg roller and then aged at 23° C. for 1 hour. The sample piece waspeeled from the glass plate at a peel angle of 90° and a peel rate of300 mm/minute with a tensile tester (Autograph SHIMAZU AG-110KN), whenthe adhesive force (N/25 mm, 80 m in length during the measurement) wasmeasured. In the measurement, sampling was performed at an interval of0.5 seconds for one measurement, and the average was used as themeasured value.

Measurement of Adhesive Force after 48 Hours at 60° C.

The sample was cut into 25 mm-wide pieces. Each sample piece was thenpress-bonded to a 0.7 mm-thick alkali-free glass plate (1737manufactured by Corning Incorporated) by one reciprocation of a 2 kgroller and then aged at 23° C. for 1 hour. The sample piece was thendried at 60° C. for 48 hours. The sample piece was then peeled from theglass plate at a peel angle of 90° and a peel rate of 300 mm/minute withthe same tensile tester, when the adhesive force (N/25 mm) was measured.

Reworkability

The sample was cut into 420 mm long×320 mm wide pieces. The sample piecewas attached with a laminator to a 0.7 mm-thick alkali-free glass plate(1737 manufactured by Corning Incorporated) and then subjected to anautoclave treatment at 50° C. and 5 atm for 15 minutes to be completelybonded. The sample piece was then heat-treated under dry conditions at60° C. for 48 hours. The sample piece (the pressure-sensitive adhesivepolarizing plate) was then peeled by hand from the alkali-free glassplate, and the reworkability was evaluated according to the criteriadescribed below. In the evaluation of the reworkability, three samplepieces were prepared by the procedure described above, and the peelingprocess was repeated three times. The evaluation criteria were as shownbelow.

-   ⊙: Three sample pieces were all successfully peeled with no adhesive    residue or no film rupture.-   ◯: Film rupture occurred in part of the three sample pieces, but it    was successfully peeled by re-peeling.-   Δ: Film rupture occurred in all the three sample pieces, but each    film was successfully peeled by re-peeling.-   x: In all the three laminates, some adhesive residue was left, or    films were ruptured and were not successfully separated every time    peeling was performed.

As used herein, the term “adhesive residue” means the state in which thepressure-sensitive adhesive undergoes cohesive fracture (parting) in abulk state so that the adhesive is clearly left on the polarizing plateside and the glass side.

Measurement of Gel Fraction

The gel fraction was evaluated using the pressure-sensitive adhesivecomposition obtained before the preparation of the sample of each of theexamples and the comparative examples. Each composition was applied to arelease-treated polyester film so that it would have a thickness of 25μm after drying. The gel fraction of each composition was measured 1hour after the application and 1 week after the application. The gelfraction was measured as described below. After the application, thepressure-sensitive adhesive was allowed to stand on the support at atemperature of 23° C. and a humidity of 65% RH. Thereafter, 0.2 g of thepressure-sensitive adhesive was sampled and wrapped in a fluororesin(TEMISH NTF-1122 manufactured by Nitto Denko Corporation) (Wa) whoseweight was measured in advance. After the fluororesin was bound so thatthe pressure-sensitive adhesive did not leak, the weight (Wb) of thewrapped product was measured, and it was placed in a sample vial. To thevial was added 40 ml of ethyl acetate. The product was then allowed tostand for 1 hour or 7 days. The fluororesin-wrapped pressure-sensitiveadhesive was then taken out, placed on an aluminum cup, and dried at130° C. for 2 hours. The weight (Wc) of fluororesin with the sample wasmeasured. The gel fraction was calculated according to formula (I): gelfraction {(Wc-Wa)/(Wb-Wa)}×100=(% by weight)

Measurement of Holding Power

The holding power (H) was measured as described below. The preparedsample was allowed to stand at 23° C. for 1 week. An upper part (10mm×10 mm) of the pressure-sensitive adhesive optical film (10 mm×30 mm)was attached to a Bakelite board through the pressure-sensitive adhesivelayer. It was then autoclaved under the conditions of 50° C. and 5 atmfor 15 minutes and allowed to stand at room temperature for 1 hour. Aload of 500 g was then applied to the lower end of thepressure-sensitive adhesive optical film. After standing for 1 hour, theholding power was determined as the length of displacement of thepressure-sensitive adhesive optical film and the Bakelite board beforeand after the application of the load.

Measurement of Refractive Index

The refractive index of the resulting (meth)acrylic polymer was measuredwith a multi-wavelength Abbe refractometer DR-M2 (manufactured by AtagoCo., Ltd.) (measurement light source: sodium lamp (589.3 nm);measurement conditions: 23° C. and 65% RH). The acrylicpressure-sensitive adhesive solution was applied to one side of asilicone-treated polyethylene terephthalate (PET) film and dried to forma pressure-sensitive adhesive layer. The pressure-sensitive adhesivelayer was laminated four times on the PET film to form a 100 μm-thicklaminate which was used as a sample for the measurement.

Surface Staining

The 25 mm sample obtained in each of the examples and the comparativeexamples was bonded to an alkali-free glass plate (1737 manufactured byCorning Incorporated) by one reciprocation of a 2 kg roller and thenaged at 23° C. for 1 hour. After the sample was peeled from the glassplate at a peel angle of 90° and a peel rate of 30 mm/minute, thesurface of the glass plate was visually observed for the degree ofstaining, based on the evaluation criteria below.

-   ◯: No staining was observed on the glass surface.-   Δ: Staining was observed on part of the glass surface.-   x: Staining was observed over the glass surface.

Punching Quality

Within 24 hours after the sample was prepared, 100 square pieces eachwith a side of 270 mm were obtained from the sample by punching. Theoperator evaluated the 100 pieces by visual observation and by touchingwith the hand with respect to whether or not the surface of thepolarizing plate side had a sticky feeling or whether or not the surfaceof the polarizing plate was stained with the pressure-sensitiveadhesive. How many pieces had a sticky feeling or a stain wasdetermined, and evaluation was performed according to the criteriabelow.

-   ◯: None of the 100 pieces had a sticky feeling or a stain.-   Δ: One to five of the 100 pieces had a sticky feeling or a stain.-   x: Six or more of the 100 pieces had a sticky feeling or a stain.

Number of Generation of Dents

Within 24 hours after the sample was prepared, 100 square pieces eachwith a side of 270 mm were obtained from the sample by punching. The 100pieces were laminated in the same direction such that the polarizingplates were placed on the upper side. The laminate was allowed to standat a temperature of 25° C. and a humidity of 55% for 1 week. Whether ornot any dent was formed and the number of dents was then determinedvisually.

-   573 : None of the 100 pieces had any dent.-   ◯: One to five of the 100 pieces had a dent or dents.-   x: Six or more of the 100 pieced had a dent or dents.

Durability

The sample was cut into 420 mm long×320 mm wide pieces. The samplepieces were bonded to both sides of a 0.7 mm-thick alkali-free glassplate (1737 manufactured by Corning Incorporated) in the crossed Nicolsarrangement with a laminator. The sample pieces were then autoclaved at50° C. and 5 atm for 15 minutes so that they were completely bonded tothe alkali-free glass plate. After this process, the sample pieces weresubjected to a process for 500 hours at 80° C., 90° C., 100° C., or 60°C./90% RH, and then foaming, peeling or separation was visuallyevaluated according to the criteria below.

-   ⊙: Neither foaming, peeling, nor separation was observed.-   ◯: Foaming (with a maximum size of less than 100 μm) was observed    with no effect on visibility.-   Δ: There were lots of foams (with a maximum size of less than 100    μm) with no effect on visibility.-   x: Foaming (with a maximum size of 100 μm or more) or separation was    observed.

Measurement of Light Leakage

The pressure-sensitive adhesive layer obtained in each of the examplesand the comparative examples was transferred and bonded to a 400 mmwide×700 mm long polarizing plate (NPF-SIG5423DU manufactured by NittoDenko Corporation) to form a pressure-sensitive adhesive layer-carryingpolarizing plate A (in which the absorption axis was parallel to thelong side of the polarizing plate). The pressure-sensitive adhesivelayer obtained in each of the examples and the comparative examples wasalso transferred and bonded to a 700 mm long×400 mm wide polarizingplate (NPF-SIG5423DU manufactured by Nitto Denko Corporation) to form apressure-sensitive adhesive layer-carrying polarizing plate B (in whichthe absorption axis was parallel to the short side of the polarizingplate). The polarizing plates A and B were bonded to both sides of a 0.7mm-thick alkali-free glass plate in the crossed Nicols arrangement andthen autoclaved at 50° C. and 5 atm for 15 minutes so that they werecompletely bonded to the alkali-free glass plate. The resulting samplewas stored at 80° C. for 500 hours and then placed on a 10,000 candelabacklight. The light leakage from the sample was visually checkedaccording to the criteria below.

-   ⊙: No light leakage was observed, and there was no practical    problem.-   ◯: Light leakage was slightly observed, but there was no practical    problem.-   Δ: Light leakage was observed, but there was no practical problem.-   x: Light leakage was significantly observed, and there was a    practical problem.

Method for Evaluation of Pot Life

The acrylic pressure-sensitive adhesive solution obtained in each of theexamples and the comparative examples was allowed to stand at atemperature of 23° C. and a humidity of 65% RH, while time was checkedfrom the preparation of the acrylic pressure-sensitive adhesive solutionto the development of an increase in its viscosity. The check was madeafter each sample was allowed to stand at a temperature of 23° C. and ahumidity of 65% RH for 6, 9, or 12 hours.

-   ⊙: No increase in viscosity was observed after 12 hours, and there    was no practical problem.-   ◯: An increase in viscosity was observed after 12 hours, but there    was no practical problem.-   Δ: An increase in viscosity was observed after 9 hours, but there    was no practical problem.-   x: An increase in viscosity was observed after 6 hours, and there    was a practical problem.

TABLE 1 Monomer Components Nitrogen- Containing Monomer Other ThanTertiary Carboxyl Weight Alkyl Aromatic Tertiary Amino Amino Group-Group- Hydroxyl Group- Average Degree (Meth)- Ring- Group-ContainingContaining Containing Containing Molecular of acrylate ContainingMonomer Monomer Monomer Monomer Weight Dis- Re- BA PEA BZA DMAEA DMAPAAAAM ACMO AA 4HBA 2HEA (×10⁴) persion fractive (parts) (parts) (parts)(parts) (parts) (parts) (parts) (parts) (parts) (parts) M_(w)M_(w)/M_(n) Index Production 80.1 19.0 0.1 — — — 0.3 0.5 — 205 3.011.484 Example 1 Production 80.0 19.0 0.3 — — — 0.3 0.5 — 200 3.23 1.484Example 2 Production 79.8 19.0 0.5 — — — 0.3 0.5 — 201 4.01 1.484Example 3 Production 80.1 19.0 — 0.1 — — 0.3 0.5 — 200 3.53 1.484Example 4 Production 79.4 19.0 0.1 — — 1.0 0.5 — 234 3.33 1.484 Example5 Production 79.6 19.0 0.1 — — 0.3 1.0 — 204 3.09 1.484 Example 6Production 78.9 19.0 0.1 — — — 1.0 1.0 — 242 3.45 1.484 Example 7Production 80.1 19.0 0.1 — — — 0.3 0.5 200 3.66 1.484 Example 8Production 75.6 19.0 0.5 — — — 3.0 2.0 — 236 2.99 1.484 Example 9Production 80.1 19.0 0.1 — — — 0.3 0.5 162 4.33 1.484 Example 10Production 80.1 19.0 0.1 — — — 0.3 0.5 — 295 3.21 1.484 Example 11Production 80.1 19.0 0.1 — — — 0.3 0.5 — 162 12.50 1.484 Example 12Production 89.1 10.0 0.1 — — — 0.3 0.5 — 220 3.68 1.476 Example 13Production 79.1 10.0 10.0 0.1 — — — 0.3 0.5 — 232 3.22 1.485 Example 14Production 64.1 19.0 16.0 0.1 — — 0.3 0.5 — 212 3.89 1.498 Example 15Production 66.1 33.0 0.1 — — — 0.3 0.5 — 215 4.01 1.498 Example 16Production 99.1 0.1 — — — 0.3 0.5 — 208 3.03 1.468 Example 17 Production44.1 55.0 0.1 — — — 0.3 0.5 — 256 3.81 1.515 Example 18 Production 80.019.0 — — — — 1.0 — 222 2.91 1.484 Example 19 Production 80.2 19.0 — — —0.3 0.5 200 4.01 1.484 Example 20 Production 80.4 19.0 0.1 0.5 211 4.231.484 Example 21 Production 79.2 19.0 1.0 0.3 0.5 204 4.52 1.484 Example22 Production 97.0 2.5 0.5 120 20.40 1.468 Example 23 Production 78.019.0 2.5 0.5 133 22.70 1.484 Example 24 Production 59.4 19.0 18.0 0.13.5 121 28.80 1.499 Example 25 Production 77.3 19.0 0.2 3.5 125 31.101.484 Example 26 Production 73.0 19.0 5.0 2.9 0.1 178 3.31 1.484 Example27 Production 73.1 26.0 0.1 0.3 0.5 251 2.89 1.490 Example 28 Production73.0 26.0  0.05 1.0 221 2.55 1.490 Example 29

In Table 1, BA represents butyl acrylate, DMAEA N,N-dimethylaminoethylacrylate, DMAPAA N,N-dimethylaminopropylacrylamide, ACMON-acryloylmorpholine, AAM acrylamide, AA acrylic acid, 4HBA4-hydroxybutyl acrylate, 2HEA 2-hydroxyethyl acrylate, PEA phenoxyethylacrylate, and BZA benzyl acrylate.

TABLE 2 Evaluations Reworkability Type and Amount Type and Amount(Adhesion)(N/25 mm) Acrylic (parts) of Isocyanate (parts) of SilaneAfter 48 Polymer Crosslinking Agent Coupling Agent Additional hours atReworkability Pot Light Type Type Parts KBM573 KBM403 Components Initial60° C. (Staining) Life Leakage Example 1 Production D160N 0.35 0.2 ⊙ 3.8⊙ 5.7 ◯ ⊙ ⊙ Example 1 Example 2 Production D160N 0.35 0.2 ⊙ 4.1 ⊙ 6.3 ◯⊙ ⊙ Example 2 Example 3 Production D160N 0.35 0.2 ⊙ 4.9 ⊙ 8.9 ◯ ⊙ ⊙Example 3 Example 4 Production D160N 0.35 0.2 ⊙ 3.9 ⊙ 5.8 ◯ ⊙ ⊙ Example4 Example 5 Production D160N 0.35 0.2 ◯ 7.5 ◯ 10.9 ◯ ◯ ⊙ Example 5Example 6 Production D160N 0.35 0.2 ◯ 7.6 ◯ 10.5 ◯ ◯ ⊙ Example 6 Example7 Production D160N 0.35 0.2 ◯ 8.2 ◯ 11.9 ◯ ◯ ⊙ Example 7 Example 8Production D160N 0.35 0.2 ⊙ 4.9 ⊙ 9.8 ◯ ⊙ ⊙ Example 8 Example 9Production D160N 0.35 0.2 Δ 9.2 Δ 14.1 ◯ Δ ⊙ Example 9 Example 10Production D160N 0.35 0.2 ◯ 7.7 ◯ 11.2 ◯ ⊙ ⊙ Example 10 Example 11Production D160N 0.35 0.2 ⊙ 3.1 ⊙ 5.2 ◯ ⊙ ⊙ Example 11 Example 12Production D160N 0.35 0.2 Δ 8.7 Δ 13.6 Δ ⊙ Δ Example 12 Example 13Production D160N 0.35 0.2 ⊙ 4.2 ⊙ 6.0 ◯ ⊙ ◯ Example 13 Example 14Production D160N 0.35 0.2 ⊙ 3.5 ⊙ 5.3 Δ ⊙ ⊙ Example 1 Example 15Production C/L 0.35 0.2 ⊙ 3.3 ⊙ 5.4 ◯ ⊙ ⊙ Example 1 Example 16Production D110N 0.35 0.2 ⊙ 3.9 ⊙ 5.5 ◯ Δ ⊙ Example 1 Example 17Production D140N 0.35 0.2 ⊙ 4.1 ⊙ 5.7 ◯ ⊙ ⊙ Example 1 Example 18Production D120N 0.35 0.2 ⊙ 4.2 ⊙ 5.9 ◯ ⊙ ⊙ Example 1 Example 19Production D127N 0.35 0.2 ⊙ 3.8 ⊙ 6.2 ◯ ⊙ ⊙ Example 1 Example 20Production D160N 0.35 0.2 ⊙ 4.0 ⊙ 6.3 ◯ ⊙ ⊙ Example 14 Example 21Production D160N 0.35 0.2 ◯ 8.1 ◯ 11.1 ◯ ⊙ Δ Example 15 Example 22Production D160N 0.35 0.2 ◯ 7.4 ◯ 11.5 ◯ ⊙ Δ Example 16 Example 23Production D160N 0.35 0.2 ⊙ 5.3 ◯ 11.5 ◯ ⊙ ⊙ Example 1 Example 24Production D160N 0.35 0.2 ⊙ 3.4 ⊙ 8.9 ◯ ⊙ ⊙ Example 28 Example 25Production D160N 0.35 0.2(KBM5103) ⊙ 2.8 ⊙ 9.4 ◯ ⊙ ⊙ Example 28 Example26 Production C/L 0.35 0.2(A100) ⊙ 5.8 ⊙ 8.0 ◯ ⊙ ⊙ Example 29 Example 27Production D160N 0.35 0.2 ⊙ 5.1 ⊙ 7.5 ◯ ⊙ ⊙ Example 21 ComparativeProduction D160N 0.35 0.2 0.2 ⊙ 3.9 ⊙ 5.8 ◯ ⊙ X Example 1 Example 17Comparative Production D160N 0.35 0.2 0.2 ◯ 8.9 Δ 14.5 ◯ ⊙ X Example 2Example 18 Comparative Production D160N 0.35 0.2 0.2 ◯ 8.0 X 22.4 ◯ ⊙ ⊙Example 3 Example 19 Comparative Production D160N 0.35 0.2 0.2 ◯ 8.5 X20.5 ◯ ⊙ ⊙ Example 4 Example 20 Comparative Production D160N 0.35 0.20.2 ◯ 8.1 X 19.6 ◯ ⊙ ⊙ Example 5 Example 22 Comparative Production D110N0.35 0.2 0.2 X 12.5 X 26.5 Δ Δ X Example 6 Example 23 ComparativeProduction D110N 0.35 0.2 0.2 X 13.5 X 23.5 Δ Δ Δ Example 7 Example 24Comparative Production D110N 0.35 0.2 0.2 X 12.1 X 27.8 Δ Δ Δ Example 8Example 25 Comparative Production D110N 0.35 0.2 0.2 X 13.3 X 25.5 Δ Δ ΔExample 9 Example 26 Comparative Production D160N 0.35 0.2 0.2 X 14.2 X25.9 ◯ Δ ⊙ Example 10 Example 27 Comparative Production D160N 0.35 0.20.2 *oligomer ⊙ 3.9 X 15.9 X ⊙ Δ Example 11 Example 1 ComparativeProduction D160N 0.35 ⊙ 3.5 ⊙ 6.7 ◯ ⊙ ⊙ Example 12 Example 1 EvaluationsProcessability Number of Durability Gel Fraction Gel Fraction GenerationPunching 60° C./ after 1 Hour after 1 Week of Dents Quality 80° C. 90°C. 100° C. 90% RH Example 1 82.1 84.5 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 2 83.2 83.3 ⊙◯ ⊙ ⊙ ⊙ ⊙ Example 3 82.9 85.5 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 4 85.5 85.4 ⊙ ◯ ⊙ ⊙ ⊙⊙ Example 5 80.2 85.2 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 6 82.2 88.6 ⊙ ◯ ⊙ ⊙ ⊙ ⊙Example 7 83.9 88.5 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 8 86.7 87.2 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example9 82.7 83.4 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 10 89.1 88.8 ⊙ ◯ ⊙ ◯ ◯ ⊙ Example 11 79.980.1 ⊙ ◯ ⊙ ⊙ ⊙ ◯ Example 12 87.5 86.9 ◯ Δ ⊙ Δ Δ ⊙ Example 13 82.1 83.1 ⊙◯ ⊙ ⊙ ⊙ ⊙ Example 14 89.0 89.9 ⊙ ◯ ⊙ ◯ Δ ⊙ Example 15 71.2 85.1 ⊙ ◯ ⊙ ⊙◯ ⊙ Example 16 90.0 92.1 ⊙ ◯ ⊙ ⊙ ◯ ⊙ Example 17 55.2 79.1 Δ Δ ⊙ ⊙ ◯ ⊙Example 18 60.9 80.3 ◯ Δ ⊙ ⊙ ◯ ⊙ Example 19 66.1 82.1 ◯ Δ ⊙ ⊙ ◯ ⊙Example 20 83.1 86.5 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 21 82.0 83.6 ⊙ ◯ ⊙ ⊙ ⊙ ⊙Example 22 81.1 84.4 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 23 83.3 84.0 ⊙ ◯ ⊙ ⊙ ⊙ ⊙Example 24 84.5 86.3 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 25 85.5 89.9 ⊙ ◯ ⊙ ⊙ ⊙ ⊙Example 26 72.0 85.1 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 27 55.7 82.9 Δ Δ ⊙ ◯ Δ ⊙Comparative 83.1 85.1 ⊙ ◯ ⊙ ⊙ ⊙ ⊙ Example 1 Comparative 85.0 84.2 ⊙ ◯ ⊙⊙ ⊙ ⊙ Example 2 Comparative 12.3 80.1 X X ⊙ Δ X ◯ Example 3 Comparative65.5 87.1 ◯ ◯ ⊙ ◯ ◯ ⊙ Example 4 Comparative 82.1 83.8 ⊙ ◯ ⊙ ⊙ ⊙ ⊙Example 5 Comparative 48.1 79.7 X X ⊙ Δ X ⊙ Example 6 Comparative 45.376.5 X X ⊙ Δ X ⊙ Example 7 Comparative 66.9 80.1 ◯ X ⊙ Δ X ⊙ Example 8Comparative 57.1 75.9 Δ X ⊙ Δ X ⊙ Example 9 Comparative 83.1 89.8 ⊙ ◯ ⊙⊙ ⊙ ⊙ Example 10 Comparative 72.1 82.1 Δ Δ ◯ Δ X ◯ Example 11Comparative 80.0 81.2 ⊙ ◯ ⊙ X X X Example 12

In Table 2, the isocyanate crosslinking agents include polyol-modifiedhexamethylene diisocyanate (D160N manufactured by Mitsui TakedaPolyurethane Inc.), polyol-modified hydrogenated xylylene diisocyanate(D120N manufactured by Mitsui Takeda Polyurethane Inc.), polyol-modifiedisophorone diisocyanate (D140N manufactured by Mitsui TakedaPolyurethane Inc.), trimer type hydrogenated xylylene diisocyanate(D127N manufactured by Mitsui Takeda Polyurethane Inc.), polyol-modifiedtolylene diisocyanate (C/L manufactured by Nippon Polyurethane IndustryCo., Ltd.), and polyol-modified xylylene diisocyanate (D110Nmanufactured by Mitsui Takeda Polyurethane Inc.); the silane couplingagent is KBM573, KBM403, or KBM5103 manufactured by Shin-Etsu ChemicalCo., Ltd., or A-100 manufactured by Soken Chemical & Engineering Co.,Ltd.; and *oligomer as an additional component in Comparative Example 12is 15 parts of an acrylic oligomer (ARFONUP-1000, 3,000 in weightaverage molecular weight, manufactured by Toagosei Co., Ltd.).

1. A pressure-sensitive adhesive composition for an optical film,comprising: a (meth)acrylic polymer comprising (a) 34 to 94% by weightof an alkyl(meth)acrylate monomer unit, (b) 5 to 35% by weight of anaromatic ring-containing (meth)acrylate monomer unit, and (c) 0.01 to0.5% by weight of an amino group-containing (meth)acrylate monomer unit,and further comprising (d) 0.05 to 3% by weight of a carboxylgroup-containing (meth)acrylate monomer unit and/or (e) 0.05 to 2% byweight of a hydroxyl group-containing (meth)acrylate monomer unit andhaving a weight average molecular weight of 1,600,000 to 3,000,000 asdetermined by gel permeation chromatography; crosslinking agentscomprising 0.01 to 5 parts by weight of an isocyanate crosslinking agentand 0.01 to 2 parts by weight of a silane coupling agent based on 100parts by weight of the (meth)acrylic polymer.
 2. The pressure-sensitiveadhesive composition according to claim 1, wherein the (meth)acrylicpolymer has a degree of dispersion (Mw/Mn) of 1 to
 10. 3. Thepressure-sensitive adhesive composition according to claim 1, whereinthe amino group-containing (meth)acrylate is a tertiary aminogroup-containing (meth)acrylate.
 4. The pressure-sensitive adhesivecomposition according to claim 1, wherein the isocyanate crosslinkingagent is a polyisocyanate compound derived from hexamethylenediisocyanate.
 5. The pressure-sensitive adhesive composition accordingto claim 1, wherein the silane coupling agent has an acetoacetyl groupor an amino group.
 6. The pressure-sensitive adhesive compositionaccording to claim 1, wherein the aromatic ring-containing(meth)acrylate is at least one selected from the group consisting ofphenoxyethyl(meth)acrylate and benzyl(meth)acrylate.
 7. Thepressure-sensitive adhesive composition according to claim 6, whereinthe phenoxyethyl(meth)acrylate makes up 5 to 20% by weight of all themonomers constituting the (meth)acrylic polymer.
 8. A pressure-sensitiveadhesive layer for an optical film, which is: a product obtained byforming a coating of the pressure-sensitive adhesive composition ofclaim 1 and subjecting the coating to a crosslinking reaction, whereinthe coating has a gel fraction of 55 to 95% and a refractive index ofless than 1.50 one hour after the formation of the coating.
 9. Thepressure-sensitive adhesive layer according to claim 8, wherein thecoating has a gel fraction of 60 to 95% one week after the formation ofthe coating.
 10. The pressure-sensitive adhesive optical film,comprising: an optical film; and the pressure-sensitive adhesive layeraccording to claim 8 formed on at least one side of the optical film.11. The pressure-sensitive adhesive optical film according to claim 10,wherein the pressure-sensitive adhesive layer has a holding power (H) of20 to 350 μm one week after the formation of the pressure-sensitiveadhesive layer.
 12. The pressure-sensitive adhesive optical filmaccording to claim 11, wherein it shows an adhesive force (F1) of 1 N/25mm to 10 N/25 mm, when it is peeled at a peel angle of 90° and a peelrate of 300 mm/minute after the steps of making it 25 mm wide, bondingit to a alkali-free glass plate through the pressure-sensitive adhesivelayer by one reciprocation of a 2 kg roller, and allowing it to stand at23° C. for one hour.
 13. The pressure-sensitive adhesive optical filmaccording to claim 12, wherein it shows an adhesive force (F2) of 2 N/25mm to 15 N/25 mm, when it is peeled at a peel angle of 90° and a peelrate of 300 mm/minute after the steps of making it 25 mm wide, bondingit to a alkali-free glass plate through the pressure-sensitive adhesivelayer by one reciprocation of a 2 kg roller, and allowing it to stand at23° C. for one hour and then dried at 60° C. for 48 hours.
 14. An imagedisplay device, comprising at least one piece of the pressure-sensitiveadhesive optical film according to claim 11.